1. Field of the invention:
This invention relates to an apparatus for successively transporting a photosensitive sheet from a roll of the sheet, more particularly to an apparatus for transporting a photosensitive sheet which comprises a buffer roller for controlling the speed of the sheet-transportation, the said apparatus being used in an apparatus for the formation of images utilizing the photosensitive sheet and an image-receiving sheet.
2. Description of the prior art:
Japanese Laid-Open Patent Publication No. 5888739 discloses a method for the formation of images which utilizes a photosensitive sheet coated with pressure-rupturable capsules containing chromogenic materials and light sensitive hardeners, and an imagereceiving sheet coated with developing materials that react with the chromogenic materials to give rise to color images.
An apparatus for the formation of images utilizing such a method usually comprises an apparatus for transporting a photosensitive sheet, in which the sheet is successively drawn out from a roll of the photosensitive sheet, and transported through a light-exposure section and a pressure-transfer section and then wound around a take up rod. The roll of the photosensitive sheet is housed in a cartridge, thereby preventing the sheet from being exposed to stray light. In such an apparatus for the formation of images, the photosensitive sheet is first exposed to light reflected from the original at the above-mentioned light-exposure section. The reflected light selectively illuminates the pressure-rupturable capsules on the photosensitive sheet so that some of the capsules receive the light and become hardened and others do not receive the light and so are left unchanged, resulting in a latent image corresponding to the image of the original. The photosensitive sheet on which the latent image has been formed is then transported to the above-mentioned pressure-transfer section, where it is brought together with the image-receiving sheet and pressure is applied thereto. Thus, the pressure-rupturable capsules that have not been hardened, rupture, and the chromogenic materials contained therein flow out onto the image-receiving sheet. Then, the chromogenic materials react with the developing materials coated on the image-receiving sheet, which gives rise to color in the chromogenic materials, thereby a colored image corresponding to the latent image being formed on the image-receiving sheet.
In the above-mentioned image-forming process of the apparatus for the formation of images, the optimum sheet-transporting speed at which the latent image can be properly formed at the light-exposure section is usually different from that at which the colored image can be properly formed at the pressure-transfer section. In general, the latter is far higher than the former; for example, the optimum sheet-transporting speed at the pressure-transfer section is about ten times as high as that at the light-exposure section. Thus, a conventional apparatus for transporting a photosensitive sheet comprises a buffer roller that can be moved to control the sheet-transporting speed so that the sheet-transporting speed can be appropriately set at the optimum level at each section.
FIG. 5 illustrates the sheet-transportation of a conventional apparatus for transporting a photo-sensitive sheet by a buffer roller. A photosensitive sheet 52 is drawn out from the roll 51 of the sheet, and transported through a transporting roller 53, a guide roller 54, a buffer roller 55, and a pair of pressure rollers 56, and then wound around a take up rod 57. The buffer roller 55 can be moved in either direction of arrow A or B. When the buffer roller 55 moves in the direction of arrow A, the photosensitive sheet 52 is drawn out from the roll 51. The direction of the sheet-transportation changes at the guide roller 54 as shown by the line of dashes and double dots. While the photosensitive sheet 52 is being drawn out, it is exposed to the light reflected from the original at the light-exposure section P1, resulting in a latent image. When the buffer roller 55 is moved in the direction of arrow B, the portion of the photosensitive sheet 52 corresponding to the latent image is transported into a pressure-transfer section p2, where the latent image is developed into a colored image to be transferred onto an image-receiving sheet as described above.
The sheet-transporting speed can be controlled by adjusting the speed of the above-mentioned linear movement of the buffer roller 55. The speed at which the buffer roller 55 moves in the direction of arrow A is set to be half as high as the optimum sheet-transporting speed at the light-exposure section P1. In the same way, the speed at which the buffer roller 55 moves in the direction of arrow B is set to be half as high as the optimum sheet-transporting speed at the pressure-transfer section.
When a new cartridge of a photosensitive sheet is placed within the body of the apparatus for the formation of images, the foremost end of the photosensitive sheet 52 is automatically transported through the transporting roller 53, the light-exposure section P1, the guide roller 54, the buffer roller 55 and the pressure rollers 56, and then wound around the take up rod 57; this is the process of automatic loading of the photosensitive sheet. If the photosensitive sheet 52 does not extend straight between the guide roller 54 and the buffer roller 55 at the time of this automatic loading of the sheet, the apparatus may become jammed with the photosensitive sheet.
Thus, the base position of the buffer roller 55, to and from which it is moved, is so located that the photosensitive sheet 52 extends substantially straight from the light-exposure section P1 through the guide roller 54 to the buffer roller 55 as shown in FIG. 5. Since the buffer roller 55 stays at this base position at the time of the above-mentioned automatic loading of the photosensitive sheet 52, the apparatus can be prevented from being jammed with the sheet.
It is assumed here that the speed at which the buffer roller 55 moves in the direction of arrow A is v1. The buffer roller 55 is moved from the base position in the direction of arrow A at a speed v1 so that the photosensitive sheet 52 may be transported through the light-exposure section P1 at a speed of 2v1, which is the optimum speed to obtain a latent image. At the beginning of this movement, however, since the buffer roller 55 starts from the base position, the portion of the photosensitive sheet 52 between the guide roller 54 and the buffer roller 55 is not transported straight but is turned along the periphery of the guide roller 54 until it comes to the straight course along the direction of arrow A. When this portion comes to the straight course to be transported straight by the buffer roller 55, the sheet-transporting speed at the light-exposure section P1 is the optimum speed 2v1. But when this portion is turning along the guide roller 54, its course is not straight so that the sheet-transporting speed at the light-exposure section P1 is lower than 2v1. In this way, at the beginning of the light-exposure step, the photosensitive sheet is transported at a speed lower than the optimum speed. Thus, the sheet-transporting speed is not stable during the period of the light-exposure step, which prevents a latent image from being properly formed, resulting in a blur in a colored image.